Definition of third-degree in English:

adjective

Those slightly farther from the center of the explosion did not die immediately, but suffered from severe third-degree burns all over their bodies, in particular to any areas that were exposed directly to the heat.

Some second-degree burns can heal with time, but deep ones and third-degree burns require skin grafts.

A third-degree burn results in the destruction of skin, and may extend into the superficial fascia, muscle and bone.